X-box binding protein 1 (XBP-1) is a basic leucine zipper transcription factor that is involved in the cellular unfolded protein response (UPR). XBP-1 is known to be active in the endoplasmic reticulum (ER). The ER consists of a system of folded membranes and tubules in the cytoplasm of cells. Proteins and lipids are manufactured and processed in the ER. When unusual demands are placed on the ER, “ER stress” occurs. ER stress can be triggered by a viral infection, gene mutations, exposure to toxins, aggregation of improperly folded proteins or a shortage of intracellular nutrients. The result can be Type II diabetes, metabolic syndrome, a neurological disorder or cancer.
Two XBP-1 isoforms are known to exist in cells: spliced XBP-1S and unspliced XBP-1U. Both isoforms of XBP-1 bind to the 21-bp Tax-responsive element of the human T-lymphotropic virus type 1 (HTLV-1) long terminal repeat (LTR) in vitro and transactivate HTLV-1 transcription. HTLV-1 is associated with a rare form of blood dyscrasia known as Adult T-cell Leukemia/lymphoma (ATLL) and a myelopathy, tropical spastic paresis.
Double-stranded RNA molecules (dsRNA) have been shown to block gene expression in a highly conserved regulatory mechanism known as RNA interference (RNAi). WO 99/32619 (Fire et al.) disclosed the use of a dsRNA of at least 25 nucleotides in length to inhibit the expression of genes in C. elegans. dsRNA has also been shown to degrade target RNA in other organisms, including plants (see, e.g., WO 99/53050, Waterhouse et al.; and WO 99/61631, Heifetz et al.), Drosophila (see, e.g., Yang, D., et al., Curr. Biol. (2000) 10:1191-1200), and mammals (see WO 00/44895, Limmer; and DE 101 00 586.5, Kreutzer et al.).